CNCing a mini mill

[d65]

What are the advantages and disadvantages of cncing a mini mill vs keeping t manual? I look foray to your responses

d65

 

[vederstein]

When I CNC"d my mini it cost more than the mill itself.

 

[kvom]

I personally think you still need a manual mill even when you have a CNC mill.

 

[RM-MN]

Some people have good hand/eye coordination and find that a manual mill works best for them, especially when doing a "one off" project as CNC takes plenty of time for setup and from then on saves time as it repeats exactly so you get multiple products that are the same. Some of us have difficulty with the hand/eye coordination and make so many mistakes in the milling that we create more scrap than true output. For us the time to make the CNC program and the troubleshooting the output is worth it. You have to decide what your purpose would be for making the mill CNC. In my case it is the combination of the hand/eye coordination and the desire to learn something new and making a mini-mill into a CNC and then learning to design in CAD and then going through the CAM fulfills that desire.

 

[d65]

I’m thing of going manual to start so I can learn basic milling skills. Almost all of my stuff willl be one off.

D65

 

[awake]

D65, if you have not done any machining, there is value in starting out on the manual machines - you will gain a "feel" (literally) for things that way, e.g., how fast you can push things, how deep a cut, etc. Do keep in mind that some of those parameters may be significantly different on a larger machine vs. a smaller machine, but some things will be universal, e.g., RPMs and SFM and such.

 

[Peter Twissell]

Plus one re. Learning to use the machine manually first.
It is quite practical to add ballscrews and servos to a mill and preserve the ability to use it in manual mode.
Perhaps even better is to add 'virtual' handles, which are just pulse generators triggering the servos. A mill fitted with these is a pleasure to use, allowing climb milling without snatching and a nice smooth feed rate independent of cutting load.

 

[CFLBob]

I've converted two mills to CNC, a micro mill (Sherline) and a 1 HP Grizzly G0704 mill.

I have to agree with the idea that learning to make some parts by hand is a good way to start. One reason is that it forces you to think of making straight cuts in X and Y - and coming up with ways to hold the part in a fixture. Holding the parts is critically important. Say you need to cut a part with a tapered side - with CNC you just tell it the start and stop points and it figures how to do it. With manual milling, you need to figure out how to do it in a straight X or Y cut.

The tradeoff is that if you're going to do a lot of parts manually, manual mills are much easier to use with Digital Read Outs - DROs - I get distracted very easily while counting rotations of the cranks. A good set of DROs will cost close to what it costs to convert to CNC.

 

[timo_gross]

A good set of DROs will cost close to what it costs to convert to CNC.

I do not agree that DROs are so expensive, entry level units cost as much as only a few ruined parts?
Good DRO-s will cost a lot, yes.

@d65: How about get started with manual.
A lot of fantastic tips out there in the Internet, what can be done with clever setups and some additional tooling. ( dividing head, rotary table, dial indicator )
I have an entry level 2nd hand hobby CNC machine. Often whish(ed) it was just a more heavy manual machine. ( weight / power wins.... )
With the manual machine all hardware for conversion can be made. Get an idea how often a CNC would solve problems, how often repetitive work is done and how often CNC creates problems.
( reading forums and fighting some stupid Software cutting where the part should be and leaving stock where the chips should fly, Computer snapping cutters were a Human operator would slow down )

Cheap CNC in doubt is not as accurate as a carefully manual operated machine. Backlash, accuracy of Electronics, Electric and Software, feedback system.

Just thought from another beginner.....

Greetings

 

[Peter Twissell]

With a little ingenuity and enough time (remember it's a hobby!) it is possible to do anything on a manual mill.

2018-06-22 11.20.10

• Peter Twissell
• Feb 26, 2020

Large profile generated using rotary table on its side and an improvised copy attachment

2018-06-24 09.16.02

• Peter Twissell
• Feb 26, 2020

Ribs generated using the same profile with a Z offset.

 

[Peter Twissell]

Incidentally, I fitted 3 axis DRO's to my mill for less than £100 total. They are the cheap, magnetic strip type, but the repeatibility is plenty good enough for my application. I still use the handwheel scales for the last couple of thou, but the DRO's are very useful to check that i'm not one full turn out, or have the backlash the wrong way.

 

[accelo]

I too have converted a Sherline. I found the mechanical process fairly straight forward with lots of help on the net.
The mechanical part of the conversion has been dropping in price.
Software is another issue. One would assume software pricing would also have dropped. Not so much, if fact it seem to be rising?
Of course there is the free stuff like Linux CNC and others.
My challenge was to find a drafting program that was compatible with everything.
Getting from the drawing to the converter to the hardware drove me nuts.
Some simple solutions out their but be prepared to pay for them.
Of course one can do it inexpensively but invariability it will be more hassle.
For me learning the software was the big headache.
Fuson 360 is great and inexpensive but I have found it overly complicated for my work and frustrating.
Rick

 

[RM-MN]

Check out FreeCAD as a design program and bCNC for the CAM and driver for the CNC operation. There are other free CAD programs too with different ways of accomplishing the same thing. It may take some experimenting to find the CNC that fits with what you want to do.

 

[wachuko]

I am in the middle of CNC my Grizzly G0704. Only reason that I am doing it is that I can't figure out how to make complex parts manually... I am better at software than I am at making parts so I figured I will be able to do what I want via software and letting the program handle the machine. My milling has been limited to very simple cuts...

I do plan to have a pendant to be able to manually control it as well. That and I got the motors with dual shaft to be able to have knobs on them (but learned afterwards that stepper motors do no like to be turned manually, reason for adding the pendant)

Simple stuff I still want to do manually myself.

As to cost, let me just say that I could have purchased a new lathe for the money I have so far in the conversion, good grief...

Here is a photo of the build I did for the electronics. Just waiting on the leadscrews to arrive to finish this conversion.

Straight cuts are simple... it is when trying to make square things round that I get confused and have lots of issues getting them right...

So to the original question... really depends on what use you are going to give your machine... I am buying tools and getting ready for when I retire in a few years... maybe I will think differently then... with more free time I might enjoy learning to manually getting parts made... but right now, because I am always in front of a computer, I tend to think that using a software solution to design and build what I want might be better for me... ...will see.

 

[wachuko]

With a little ingenuity and enough time (remember it's a hobby!) it is possible to do anything on a manual mill.

2018-06-22 11.20.10

• Peter Twissell
• Feb 26, 2020

Large profile generated using rotary table on its side and an improvised copy attachment

2018-06-24 09.16.02

• Peter Twissell
• Feb 26, 2020

Ribs generated using the same profile with a Z offset.

I hope to, some day, be able to make something like that... very cool indeed!! And manually done... wow...

One of the reasons I joined this forum. I am just amazed of what folks have made and shared here...

Looking forward to learning how to do the same...

 

[ddmckee54]

wachuko:

You said "but learned afterwards that stepper motors do no like to be turned manually, reason for adding the pendant."

I'm guessing that you tried moving the motor while the stepper driver was turned on and enabled, and that the motor did not want to turn? If so, the stepper driver was doing it's job and keeping the motor from turning when the motor is stopped. When I want to move an axis manually I disable that stepper driver, the motor is then free to turn normally. You will feel the motor ratchet slightly as it turns between steps, but this is normal for a stepper motor.

Don

 

[awake]

One concern I have had with turning a stepper motor by hand (de-energized, as Don notes), is that, as I understand it, turning the motor generates an electrical pulse. Somewhere or other I have read cautions about smoking the electronics this way on a 3d printer - don't know if that would apply to a more robust setup such as pictured above.

 

[RM-MN]

One concern I have had with turning a stepper motor by hand (de-energized, as Don notes), is that, as I understand it, turning the motor generates an electrical pulse. Somewhere or other I have read cautions about smoking the electronics this way on a 3d printer - don't know if that would apply to a more robust setup such as pictured above.

You are quite right, turning the motor generates electricity as I discovered when I pushed the table on my 3D printer back quickly. That caused the display screen to light up. No damage was discovered but I'm a little more careful at how fast I push the table back now. Turning it slowly keeps the voltage produced quite low. One would not normally turn it fast enough to do damage by hand.

 

[John Antliff]

I have never thought of that possibility! I have been hand positioning my router table axis's without any damage for many years! I prefer moving them by hand rather than jogging them. I have even moved them when they have been activated when I have tried to "nudge" an axis slightly to compensate for lost steps (not very effective and I usually had to do the job again).

 

[awake]

RM-MN makes a very good point - speed of movement is going to affect the amount of energy produced. Yeah, probably not going to be highly effective to "nudge" an energized stepper!